2nd International Workshop of Structural Health Monitoring, Sept. 8-10, 1999,
Stanford University.
Title:Recent Progress in the Application of E/M Impedance Method to Structural Health Monitoring, Damage Detection, and Failure Prevention
Authors:Victor Giurgiutiu1
Craig A. Rogers2
ABSTRACT1
Recent progress in the application of the electro-mechanical (E/M) impedance method to structural health monitoring, damage detection, and failure prevention is prented. A brief review of the E/M impedance method principles is followed by applications to bolted and spot-welded structural joints, and to polymeric composite overlays to construction engineering structures. The modeling of the interaction between the piezoelectric active nsor and the host structure is described. The development of a meaningful structural damage index that can identify the damage prence, location, and magnitude is treated, and veral recent works, including neural networks approach, are cited. Co
nclusions and suggestions for further work, and relevant bibliography are included.
1.INTRODUCTION
1.1BACKGROUND
The electro-mechanical (E/M) impedance method for structural health monitoring, damage detection and failure prevention is a new technology utilizing the emitter-detector properties of active material nsors and the structural drive-point mechanical impedance (Rogers and Giurgiutiu, 1997). In previous work (Giurgiutiu and Rogers, 1997), the authors showed that changes in the high-frequency drive-point mechanical impedance can be nd in the form of changes in the apparent E/M impedance of the active material nsor. This allows the direct monitoring of impedance changes induced by structural damage. No intermediate equipment between the active nsor and the impedance analyzer is needed. A number of situations have been considered for using the E/M impedance method in conjunction with active material nsors to health monitoring and failure prevention applications. Recent work performed with the E/M impedance technique at the University of South Carolina encompass damage detection and health monitoring of bolted joints, spot-welded joints, and of the joint between the concrete substrate and a polymeric composite overlay. Th
e bolted joints were lected becau damage in the joint can be easily induced and subquently removed. This reversibility aspect allows for testing the method repeatability, which is esntial for method validation. Aluminum thin-gauge plates and multi-site bolt-washer-nut asmblies were ud in the experiments. The study of spot-welded joints was performed using fatigue loading of shear lap-tension specimens. In the experiments, gradual propagation of damage, induced by the fatigue loading, was monitored with the stiffness-damage correlation technique. Thus, direct mapping between damage progression and the RMS E/M impedance change was achieved. The propagation of cracks in the adhesive bond between composite overlays and concrete substrates was monitored with an array of nsors affixed onto or embedded into the composite. Correlation between damage progression (crack advancement) and RMS impedance change was established.
howtobehavewellModeling efforts were directed at understanding the subtle interaction between 1Associate Professor, Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29208, victorg@sc.edu, 803-777-8018, Fax 803-777-0106.
2Professor and Dean, College of Engineering, University of South Carolina, Columbia, SC 29208.
the two entities with patently different impedances: the minute active nsor and the large host struct
ure. Although the magnitude of the respective impedances is veral orders of magnitude different, careful examination of their real and imaginary parts revealed that the real parts become commensurable around high-frequency resonances. Thus, the high-frequency mechanical behavior of the structure is directly reflected into the electro-mechanical impedance respon.Another important aspect discusd in the paper is that of developing a meaning damage index that could adequately identify the prence, location, and magnitude of structural damage. Several efforts are cited, some including neural networks.The results prented in this paper are further proof of the suitability of the E/M impedance method for structural health monitoring, damage detection and failure prevention. Directions for further work are charted in the conclusions.1.2
西方情人节
PRINCIPLES OF THE HIGH FREQUENCY ELECTRO-MECHANICAL (E/M) IMPEDANCE METHOD
Consider a piezo-electric active nsor in intimate contact with a host structure.When excited at high frequency (typically 100 to 800 kHz), the active nsor nds and receives high-frequency elastic waves through its nsor/actuator functions.
Figure 1
四级答案2021
Electro-mechanical coupling between the PZT transducer and the
structure.
滚轧机The structural drive-point mechanical impedance,ωωωωωω/)()()()(e e e str ik c m i Z −+=, (Figure 1) interacts with the internal impedance of the transducer, PZT Z , and generates a combined impedance respon,)(ωZ , as shown in Equation (1). Thus, the structural drive-point mechanical impedance (itlf dependent on the state of structural damage) is reflected into the electrical impedance as en at the transducer terminals.
1
2
31)()()()(−ùêë
é÷÷øöççèæ−ωωωκωωstr PZT str Z +Z Z 1 C i =Z .(1)In Equation (1), )(ωZ is the equivalent electro-mechanical admittance as en at the PZT transducer terminals, C is the zero-load capacitance of thpaparazzi
e PZT transducer,and κ31 is the electro-mechanical cross coupling coefficient of the PZT transducer (33111331/εκs d =). The electro-mechanical impedance method is applied by scanning a predetermined frequency range in the hundreds of kHz frequency band and recording the complex impedance spectrum. By comparing the impedance spectra taken at various times during the rvice life of a structure, meaningful information can be extracted pertinent to structural degradation and the appearance of incipient damage. It must be noted that the frequency range must be high enough for the signal wavelength to be compatible with the defect size. Experiments that have proven the ability of the E/M impedance technique to detect damage in a variety of applications are described next.
roam
(a)
(b)
Figure 2High-frequency electro-mechanical impedance health-monitoring testing of bolted joints: (a) Four shear lap joint tension specimens. (b) Clo-up
pleasureview of tone of the joints showing bolt-heads, washers, and the two PZT
active nsors (Giurgiutiu, Turner, and Rogers, 1999)
2.HIGH-FREQUENCY E/M IMPEDANCE MONITORING OF BOLTED
JOINTS
The successful performance of damage detection experiments rests upon the ability to create control
led damage specimens. Generally, the creation of damage is an irreversible process that needs to be performed with utmost care. However, a special situation aris in the ca of bolted joints. In bolted joints, damage can be created and also eliminated by modifying the bolted joint parameters, such as the tension in the bolt, or the prence/abnts of stiffening washers. Figure 2 prents experiments performed to correlate the E/M impedance readings with the prence of damage in the most common structural joint – the bolted joint. Results of the investigations are shown in Figure 3.airraid
Figure 3Results of the high-frequency electro-mechanical impedance health monitoring testing of bolted joints: (a) electro-mechanical impedance
signatures for three structural health situations: no damage (bolt +
washer); partial damage (bolt only); extensive damage (no bolt). (b)
Correlation between RMS impedance change and specimen structural
health (damage progression). (Giurgiutiu, Turner, and Rogers, 1999)
3.HIGH-FREQUENCY E/M IMPEDANCE MONITORING OF SPOT
Figure 5Results of spot-welded joints health monitoring: (a) E/M impedance
loss (damage progression) (Giurgiutiu, Reynolds, and Rogers, 1998).
aesthetically4. HIGH-FREQUENCY E/M IMPEDANCE MONITORING OF
COMPOSITE OVERLAYS ON CONCRETE STRUCTURES Composite overlays are thin sheets of fiber reinforced polymeric material (1/8-in to 1/4-in) adhesively bonded to conventional construction engineering materials.The composite may be applied as: (a) wet lay-up; or (b) precured panels; or (c)partially cured prepregs. For wet lay-up and prepreg systems, the adhesive is the polymeric resin itlf. For precured rigid panels, parate adhesive material needs to be ud. Structural upgrades with composite overlays offer considerable advantages in terms of weight, volume, labor cost, specific strength, etc. However,one critical issue is the still unknown in-rvice durability of the new material systems. Their ability to safely perform after prolonged exposure to rvice loads and environmental factors must be ascertained before wide acceptance in the construction engineering community is attained. Several investigators have reported the u of E/M impedance method to monitor cracks and disbonds in composite overlay systems on civil structures (Quattrone, Berman, a
nd Kamphaus,1998; Raju, Park, and Cudney, 1998).
(a)
四级单词(b)
Figure 6University of South Carolina test specimen for E/M impedance technique
disbond detection: (a) support fixture, concrete brick and composite
overlay; (b) retention bolts (Giurgiutiu, Whitley, and Rogers, 1999).
Composite
overlay Concrete substrate Support
fixture
PZT active nsors
